70hp Force surging under load (video)

[art_dodger]

Hey all,

I have a 1992 70hp Force outboard on a 17' Maxum that continuously "surges" when under load. If I have any more than a couple of people in the boat, or try pushing the boat through the water below planing speed, the motor surges continuously. If I'm at idle, traveling at low speed, or once I get the boat up to plane, the surging stops and the motor appears to be running smoothly.

It has been doing this for quite some time, so I don't believe it is related to gasoline quality, etc. I just had it pretty much rebuilt last week due to a blown piston - I thought after replacing 2 pistons & having the cylinder walls honed that the problem might disappear but no such luck...

Rather than attempting to describe the surging, I've uploaded a short video to YouTube that I made this morning that gives a pretty clear indication of what I'm talking about - I would sincerely appreciate if someone might provide me with any suggestions as to what might be causing this problem.

The video:
http://www.youtube.com/watch?v=cehqGD-MfG0
Thanks - Dodger

 

[bertthedefender]

Re: 70hp Force surging under load (video)

Hi Dodger, looks like we have the same package - I have a 1991 Maxum 1700XR Bowrider with the 70hp Force motor.

When it was rebuilt, did you change the fuel pump? What condition is it in? Could it be a sticking needle or float in the carb? Whats the condition of the primer bulb?

Just a few things that could be worth checking!

 

[roscoe]

Re: 70hp Force surging under load (video)

I would look at fuel delivery.
Also, check the carb-intake gasket or the intake to powerhead gasket, looking for air leak.

 

[art_dodger]

Re: 70hp Force surging under load (video)

Both excellent suggestions - No, I don't belive they rebuilt the fuel pump - I just dropped $1500.00 on it last week having #1 & #2 pistons replaced & cylinders honed (as well as a new impeller & seals for the lower end) so I'm hoping it's something inexpensive this time - Fuel pump rebuild & a carb kit I can handle myself...

The motor seemed like it had been surging like this for some time, well before last week's rebuild... I had the intake manifold & carb off just prior and both the manifold & carb gaskets are like new - More & more I'm also suspecting fuel pump or the carb itself.

I haven't tried squeezing the bulb while it's surging to see if it changes - I guess if I do so and it smooths out, that would indicate a fuel pump problem? Is there anything else I should try to attempt to isolate the problem?

Thanks for the replies so far!

Dodger

 

[jaqnut]

Re: 70hp Force surging under load (video)

I'm almost certain that your problem is your fuel / water separator. I have a '93 1700 XR / Force 70 and I had a similar problem. After a little bit of time in rough water it would start losing RPM erratically, almost as if it were experiencing vapor lock. I checked everything I could think of, water in the tank, etc. but couldn't find the problem. I replaced the water separator filter and that didn't help.

Finally I ran across a separator bracket that had an extender on the fuel pickup. Apparently, foam was building up at the top of the separator and causing fuel starvation. A simple plastic extender was enough to get below the foam. I haven't had a problem since. I only know of one company that makes this product; my first try posting I included a link, and my post never appeared. Maybe it was interpreted as an ad. Post back for further info.

Anyway, I'd bet a lot that its the separator, but if you want to do a little more testing before you cut into your fuel line, you could try an above deck six gallon straight in to the outboard. If the problem goes away, you've isolated the problem to your boat's internal fuel system.

Good luck...post back next season if it works.

 

[art_dodger]

Re: 70hp Force surging under load (video)

Thanks for the suggestion... After some considerable wrangling, I finally managed to get all the parts for a carb rebuild from Tillotson in Ireland, plus I've got the rebuild kit for the fuel pump now as well.

The boat is winterized & put away for the winter, but once the white stuff leaves in the spring, I'll be rebuilding both. Hopefully, one of the two rebuilds will resolve the issue - If not, back to the drawing board!

Thanks again for the continued suggestions...

Dodger